<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8" />
		<title></title>
	</head>
	<body>
		<button class="btn" id="box">点我</button>
		<div>不要点</div>
		<script type="text/javascript">
			document.querySelector(".btn").onclick = function(){
				alert("弹窗")
			}
		</script>
	</body>
</html>
